What characteristic morphologic forms help identify this
pathogen?
Size and broad based budding, refractile thick cell wall.
What are risk factors for acquisition of this organism, and what is
the portal of entry?
- Exposure to soil and warm moist wooded areas rich in organic
debris increase the risk of exposure to Blastomyces.
- Inhalation of
conidia and conversion to yeast phase in the lung provide the most
common portal of entry, with skin lesions being a manifestation of
dissemination; however primary skin disease after dog bites has been
reported.
What are the major host defenses against this pathogen?
- Inhaled conidia are phagocytized and killed by neutrophils ,
monocytes and macrophages .
- The yeast forms are more resistant to
phagocytic killing ; hence, conversion to yeast forms represents a
virulence characteristic of B dermatitidis.
- T cell mediated responses
are important .
- Humoral immunity has no demonstrable protective effect.
What clinical syndromes are caused by this pathogen?
- Pneumonia and empyema, ulcerated or verrucous lesions of the
skin which may mimic carcinoma, subcutaneous nodules, bone and joint
involvement, prostatitis and brain abscess are seen .
- Disseminated
infection is more frequent in immunocompromised hosts, in particular in
HIV disease.
What diagnostic procedures are helpful?
- Demonstration of characteristic yeast forms in clinical
specimens and silver stains are helpful .
- Presence of pyogranulomas or
pseudoepitheliomatous lesion of the skin or upper respiratory tract
should prompt a search for B. dermatitidis.
- Culture on Saborauds or
enriched media may take upto 4 weeks to grow .
- Conversion of the
mycelial form into the yeast phase is required for confirmation of the
diagnosis.
- Serologic tests lack sufficient positive or negative
predictive value to be of use in routine clinical practice.
What is the treatment of choice?
- In severely ill patients or immunocompromised patients,
especially in the presence of CNS involvement, treatment with
amphotericin B is preferred.
- In immunocompetent hosts with mild to
moderate disease itraconazole or ketoconazole may be used.